In an internal combustion engine a boost in horsepower can be accomplished by forcing a more dense air/fuel charge into the cylinders with a supercharger. A supercharger provides a simple, dependable and affordable method of increasing horsepower and torque.
A supercharger forces a more dense air/fuel mixture into an engine's cylinders than the engine can draw in under normal conditions. This higher-energy mixture produces more power. Supercharging increases the engine's volumetric efficiency without increasing its displacement. Therefore, a small engine can produce the horsepower and torque of a relatively larger engine.
There are three basic blower systems available: turbocharging, positive displacement supercharging, and turbine-type supercharging. Turbocharging places a turbine wheel in the exhaust flow. The turbine blades are directly connected to a centrifugal blower. One major disadvantage of a turbocharger is "turbo-lag." This is the delay that occurs after calling for power with the throttle before the rotational speed of the system "spools up" to deliver that power. Turbochargers are difficult systems to properly adapt and tailor to an engine. An improperly sized or designed turbo system can rapidly over-boost and ruin a spark-ignited engine. The "sizing" of the turbo to the engine, and the matching of the turbine size and design to impeller size and design is very critical in a turbo application. Additionally, the exhaust turbine tends to cool the exhaust gases thereby delaying the catalyst "light-off" of modern automotive emissions systems.
The most common positive displacement system is the "Roots blower" in which a belt-driven shaft drives two close-tolerance rotors which are geared together. Each full rotation sweeps out a specific fixed volume, unlike the fan-like characteristics of a turbine device.
Turbine-type supercharging is a system having a drive-belt from the crankshaft. A speed-increaser, either geared or gearless, is required to multiply the speed of the turbine impeller relative to that of the input shaft. The delivery of a turbine-type device varies dramatically with its rotational speed, and is prone to under-boost at low speed and over-boost at high speed. An example of a centrifugal turbine supercharger is disclosed by M. Shirai in U.S. Pat. No. 5,158,427.